Railway track circuit apparatus



April 8, 1941.

B. E. OHAGAN 2.237,789

RAILWAY TRACK CIRCUIT APPARATUS Filed Feb. 13, 1940 a BX H15 ATTORNEY atented Apr. 8, 1941 UNITED STATES PATE'l RAILWAY TRACK CIRCUIT APPARATUS Application February 13, 1946, Serial No. 318,746

20 Claims.

My invention relates to railway track circuit apparatus; and it has particular reference to the organization of such apparatus into railway track circuits having increased sensitivity to train shunts.

I am aware that it has been proposed heretofore to increase the shunting sensitivity of track circuits by controlling track relays through the medium of three-element electronic devices or tubes having their grid or control element supplied with energy from the rails of the trackway. In such systems, it is generally necessary in order to provide a normally energized system wherein the track relay is energized when the track circuit is unoccupied and is deenergized when the track circuit is occupied, to provide an initial biasing force on the grid of such value that the tube is rendered nonconducting in response to such biasing force but is rendered conducting when such force is opposed by energy derived from the trackway. In order to provide the customary safety features inherent in the ordinary track circuits, systems employing threeelement electronic tubes generally require that additional means be incorporated therein for checking the integrity of the tube elements and of the biasing electromotive force, since it is evident that a failure of such tube or of the biasing electromotive force might remove the tube and hence the relay from control by the trackway energy.

An object of my present invention is to incorporate electronic devices into railway track circuits in a novel and improved manner such that the track relay is effective to check the ini tegrity of the tube elements.

Another object of my invention is to incorporate electronic devices into railway track circuits of the normally closed circuit type in such manner that the devices are controlled by tracki porate into track circuits novel and improved means for maintaining the track relay at its proper energy level irrespective of relatively wide variations in track ballast resistance.

A still further object of my invention is to provide novel and improved forms of railway track circuits.

I propose to achieve the above-mentioned and other important objects and characteristic features of my invention which will become readily apparent from the following description, by controlling a track relay through the medium of a thermionic device having its heating element controlled by energy received from the track rails. In certain forms of my invention shortly to be described, an independent source of energy is provided for the track relay and is connected across the elements of the electronic device,which device functions to pass current derived from such source if the filament or heating element of the device is supplied with trackway energy. In other forms of my invention, the energy for energizing the heating element of the electronic device and the energ for controlling the track relay are both derived from the trackway. In such latter forms, the electronic device functions as a valve for controlling the supply of energy to the track relay in accordance not only with the amount of trackway energy passed by the tube and available to energize the relay, but also in accordance with the amount of trackway energy available to energize the heating element of the electronic device.

The invention further consists in the parts and in the arrangement and organization of the parts, as will be pointed out in detail presently.

I shall describe several forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. l is a diagrammatic view illustrating certain characteristics of an electronic device of the thermionic rectifier type. Fig. 2 is a diagrammatic view illustrating a preferred form of apparatus embodying my invention. Figs. 3 to 8, inclusive, are dia-' grammatic views each showing a modified form of the apparatus represented in Fig. 2 and each also embodying my invention. In each of the several views of the drawings, similar reference characters have been employed to designate corresponding parts.

Referring first to Fig. l, the diagram constituting this view represents a typical transfer characteristic curve of electronic devices or tubes of the rectifier type in which an evacuated or a gas-filled container encloses a cathode, which must be energized or heated to condition the tube for operation, and one anode in the case of a half-wave rectifier or two anodes in the case of a full-wave rectifier. The diagram represented in Fig. 1 is plotted between filament or heating voltage as abscissa and anode current as ordinate, and represents the non-linear transfer characteristics of tubes of the class mentioned when the anode voltage is held constant. It is to be noted that substantially no current is passed by the tube in the lower voltage range of the filament but that after the filament voltage reaches a certain value, which I shall term the "starting voltage, a slight increase in such voltage then effects a much larger increase in current passed by the tube. In similar manner, it can be seen that if the heater voltage is just above the starting value so that the tube is effective to pass current, a slight reduction in such heater voltage causes the tube substantially to cut off and become ineffective to pass current.

I have represented in Fig. 2 a preferred form of apparatus in which the non-linear characteristics of tubes of the class mentioned are utilized to provide track circuits extremely sensitive to train shunts. Referring now to Fig. 2, the reference characters I and la designate the track rails of a stretch of railway track divided by means of the usual insulated rail joints 2' interposed in the rails at D and at E, into an insulated section of track DE. Trackway energy is supplied to the rails of section D-E, preferably adjacent one end of the section, from any suitable source of current such as a track battery 3, which battery as shown is connected across the rails I and la adjacent end E of the section in series with the usual current limiting impedance 4.

The reference character T designates a thermionic device of the class previously mentioned and comprising either an evacuated or a gas-filled container 5 in which are disposed two elements or electrodes, one of which is a cathode 6 and the other of which is an anode 1. Device T is characterized by the fact that when an electromotive force of a given magnitude is impressed across its cathode and anode, the device is conditioned to pass current in response to such electromotive force when and only when its cathode 6 is heated and anode 1 is positive with respect to cathode 6.

and the amount of current flowing in such device is dependent within limits upon the heating or filament voltage of the device. As shown, thermionic tube T may be of the directly heated cathode type in which the heating electromotive force is applied to the cathode element so that such element functions also as a filament, or if desired, an indirectly heated cathode type may be employed in which the cathode is heated through the medium of an independent heating element or filament located adjacent the cathode and sup plied with the heating electromotive force.

The reference character TR designates a relay interposed in a circuit which is connected across the two elements of tube T and which is supplied with an electromotive force of the previously mentioned given magnitude from a suitable source of anode circuit current, such for example as a battery not shown but having its opposite terminals designated by the reference characters B and C. The polarity of this anode circuit source is so selected that anode I constantly is positive with respect to cathode 6, and it follows that in accordance with the degree of energization of cathode 6, the tube T is effective to pass current between its two electrodes due to the applied electromotive force and hence tube T is effective to control the energization of relay TR.

Relay TR may be made responsive to traflic conditions in section DE and hence may be made to function as a track relay by utilizing the trackway energy supplied to the rails of section DE by battery 3 for controlling energization of the heating element of tube T. As shown in Fig. 2, the heating element or cathode 6 of the tube may be connected directly across the track rails I and la of section DE adjacent end D so that the degree of energization of the cathode is made dependent upon traific conditions in the section. In this form of my invention, the parts preferably are proportioned so that when section DE is unoccupied, the electromotive force supplied to the track rails l and la by track battery 3 is effective to establish across the heating element of tube T a voltage above the starting voltage of the tube and sufiicient to control the tube to such point on its performance curve that enough current is passed by the tube due to the anode circuit source to effectively energize relay TR. Relay TR accordingly is held energized when section DE is unoccupied.

Under the above assumed conditions, the voltage drop across the heating element of tube T is relatively large with respect to the output voltage of the trackway source. It can be seen, there fore, that when a train enters section DE and establishes a shunt across the rails of section DE, the voltage applied to the heating element of tube T is greatly reduced and consequently the amount of current passed by the tube is reduced to a value below that required to hold relay TR energized. Relay TR accordingly is caused to be released in response to the presence of a train in section DE.

It should be noted that the non-linear transfer characteristics of tube T are such that the apparatus of Fig. 1 is effective to control relay TR to a released condition in response to relatively poor or high resistance train shunts. For example, it can be seen from an inspection of the curve represented in Fig. 1 that it is not necessary to reduce the heater voltage of tube T to a relatively low value in order to control the anode circuit current to a correspondingly relatively low value, but it is only necessary to reduce such heater voltage to a value below the cut-off volta e. that is. the heater voltage at which the anode circuit current becomes substantially zero. Accordingly, it can be seen that the train shunt to be effective with the apparatus of Fig. 2 is required to reduce the heater voltage of tube T only the slight amount necessary to bring the tube below its cut-off voltage, hence such train shunt need be effective to by-pass only the increment of voltage above the cut-off voltage of the tube. It is readily apparent that relatively ineffective or high resistance train shunts, which might be ineffective to properly shunt a track relay connected directly in circuit with the track rails, are effective to cause the apparatus of Fig. 2 to release the track relay. It follows, therefore, that apparatus embodying my invention provides a railway track circuit of the normally closed circuit type extremely sensitive to train shunts.

Fig. 3 represents a modified arrangement of the apparatus of Fig. 2. wherein the track battery 3 of Fig. 2 is replaced by a track transformer TT having its primary winding ii) supplied with energy from a suitable source of alternating current, such as a generator not shown but Whose opposite terminals are indicated by the reference characters BX and GK, and having its secondary winding Ii connected across the rails I and la in series with a current limiting impedance l2. The heater element 6 of tube T of Fig. 3 is supplied with trackway energy through the.medium of a receiving transformer RT which has its primary winding is connected across the track rails I and la and has its secondary winding l4 connected across the terminals of cathode 6 of tube T. Relay TR of Fig. 3 is connected across the cathode and anode of tube T in a circuit sup plied with alternating current from a source designated by the reference characters BX and UK. It is believed that the operation of the apparatus of Fig. 3 will readily be apparent from an inspection of Fig. 3 together with the foregoing description of the apparatus of Fig. 2, and further detailed explanation is deemed unnecessary except to point out that tube T of Fig. 3

functions as a half-wave rectifier and passes current to energize relay TR during each half cycle of the alternating current that anode T is positive with respect to cathode it.

An advantage of the tract. circuit shown in Fig. 3 is that receiving transformer RT provides means whereby the track rails of section DE may be supplied with alternating trackway energy of relatively low voltage, thus keeping down the current leakage across the trackway ballast, and such low voltage trackway energy may he stepped up by properly proportioning receiving transformer RT so that the proper filament voltage may he applied to control tube T.

A nother modification of the apparatus of Fig. 2 is shown in Fig. 4, wherein a receiving transformer RTi is employed to provide not only the filament voltage but also functions as the source of electroinotive force for theanode circuit of the tube. In Fig. 4:, cathode ii of tube T is connected in circuit with a portion of secondary winding l5 of transformer RM and hence is supplied with heating current whenever section DE is unoccupied. Relay TB is connected across the cathode and anode of tube T in series with another portion of winding iii of transformer RT!, and as a result the supply of current to the anode circuit of tube T and to relay TR is derived from the track rails, It can be seen that when section D--E becoi occupiedthe train shunt in. the section is eifective to shunt energy away from both the heating element and the anode circuit of tube T. Inasmuch as the amount of current passed by the tube dependent both upon the heater voltage and upon the voltage of the source connected across its electrodes, it is apparent that when the voltages applied across the heater and the anode circuits are both reduced in magnitude by a train shunt in the section, the amount of current passed by tube T is reduced to an even greater degree by a relatively poor or high resistance train shunt than if the train shunt controls only the filament voltage. It follows, therefore, that the apparatus of Fig. a provides a track circuit having greatly increased shunting sen sitivity,

Another advantage of the apparatus illustrated in Fig. 4 is-that the energy supplied to the anode circuit of the thermionic tube and to the relay is derived from the track rails and as a result no separate or auxiliary source of energy is re quired for the anode circuit of the tube. Accordingly, it is evident that if for any reason the tube fails so that the tube electrodes become short circuited, the entrance of a train on the section and the resultant train shun-t is effective to reduce the energization of the tube filament and of the anode circuit so that relay TB. is released in response to such train shunt. It follows, therefore, that the apparatus of Fig, 4 operates on the closed circuit principle, whereby a failure of a part of such apparatus to function properly will not interfere with the proper operation of the track. relay in response to a train shunt.

I have represented in Fig. 5 one manner in which track circuit arrangements employing an alternating current source for the anode circuit of the recffying tube may be modified to utilize a full-wave rectifying tube Tl rather than the half-wave tube T hereinhefore described. Referring now to Fig. 5, which represents the track circuit arrangement of Fig. 4 modified to incorporate a fulhwave rectifier tube Tl, it can be seen that tube Ti may be utilized by connecting its two anodes l and la in circuit with the anode circuit source in such manner that such anodes alternately are made positive with respect to cathode 6 during the opposite half cycles of the anode circuit source. As shown, this arrangement may be achieved by employing a center- .tapped secondary winding it on a receiving transformer RTZ; connecting the two ends of such winding to anodes l and la, respectively, of the tube; and interposing relay TR in circuit between the center tap of winding 16 and one side of cathode 8. The filament or heating voltage of tube T! is derived from an independent secondary winding H of transformer RTZ,

It is believed that the manner in which the apparatus of Fig. 5 functions to control the energization of relay TR in response to trafllc conditions in section DE will readily be apparent from an inspection of the drawing together with the foregoing description of the operation of the apparatus of Fig. 4, and further detailed explanation is deemed unnecessary except to point out that anodes I and Ta of tube Ti are alternately caused to become positive with respect to cathode E in response to the trackway energy derived by transformer RTE from the rails of section D-E, so that as a result the tube functions as a full-wave rectifier to supply relay TR with full-wave rectified current during each cycle of the alternating current.

Figs. 6, '7 and 8 each represent track circuit arrangements embodying my invention and incorporating means for maintaining the track relay at its proper energy level irrespective of the usual track ballast resistance variations such as might be encountered in practice. In Fig. 6 a saturable reactor SR is employed to compensate for ballast resistance variations by varying in accordance with the energization of the track relay, the impedance of a main or alternating current winding 19 connected in parallel with primary winding E3 of receiving transformer RT! across the track rails at the track relay end of the section. This control of the impedance of winding It may be effected by supplying energy to the track relay through a control or saturation winding 18 mounted together with winding IS, on a magnetizable core of the saturable reactor.

Referring now to Fig. 6, which illustrates for example the track circuit arrangement of Fig. 4 modified to incorporate the saturable reactor SR, the main or alternating current winding IQ of the reactor is shown connected across the rails l and la, adjacent the relay end D of the section, and winding it) of the reactor is shown interposed between secondary winding 55 of transformer RTI and the winding of relay TR. The

parts of the apparatus of Fig. 6 are designed and proportioned so that under the most unfavorable ballast conditions expected to be met in practice, the energy supplied from the track rails to relay TR is that necessary to provide the desired energization of relay TR and this current flowing in winding I8 of the reactor so controls the permeability of the magnetizable core of reactor SR that the impedance of winding I9 is relatively high and as a result relatively little of the trackway energy available is shunted by Winding I9 away from primary winding I3 of receiving transformer RTI. Furthermore, the parts are so proportioned that the flux created in the core of reactor SR due to current in winding I8 controls the permeability of such core to a value for which small increases in the flux will cause comparatively large decreases in the impedance of winding I9. It can be seen, therefore, that as the ballast resistance increases so that a higher energy level is present in the rails I and Ia to cause a correspondingly higher voltage to be induced in secondary winding I5 of transformer RTI, the increased energization of winding I3, which is connected in series with relay TR across secondary winding I5 of transformer RTI, varies the permeability of the magnetizable core of reactor SR in such manner as to decrease the impedance of winding I9, so that as a result more of the trackway energy is shunted by winding I9 away from the primary winding of transformer RTI. By properly proportioning the parts of reactor SR, it is readily apparent that the reactor may be made to function to prevent excessive energization of relay TR under high ballast resistance conditions by varying the impedance of winding I9 of the reactor to cause that winding to function as a variable shunt which shunts away the increment of trackway energy above the value necessary to hold relay TR energized. Relay TR accordingly is held energized by the apparatus of Fig. 6 at substantially a constant energy level irrespective of relatively wide variations of track ballast resistance.

In Fig. '7, compensation for ballast resistance variations is effected by employing a saturable receiving transformer R'I'3 which comprises a magnetizable core 20 upon which are mounted a primary winding I3 receiving energy from the l track rails, a secondary winding I5 supplying energy to the filament and to the anode circuit of tube T, and a control or saturating winding 2 interposed in series with the track relay TR in the anode circuit of tube T and efiective to control the inductive coupling of the transformer primary and secondary windings.

In a preferred construction of the saturable transformer RT3, as shown in Fig. '7, the magnetizable core 20 is arranged with three parallel legs M, 22 and 23 connected together at top and bottom; the primary winding I3 comprises two coils I311. and I3?) disposed on the upper end of core 20 on either side of the middle leg 22 and connected in series in such manner that both coils circulate flux in agreement in a magnetic circuit including the two outer legs of the core in series; the secondary winding I5 comprises two pairs of two coils each, one coil of each pair disposed on the lower end of core 20 on either side of middle leg 22; and the saturation or control winding 24 is disposed on middle leg 22 of the core. The four coils of the secondary winding I5 are connected in series with each other in such manner that electromotive forces induced Cir therein in response to the alternating flux set up by primary winding I3 are additive, and these four coils are connected to one side of cathode 6 of tube T and are connected through winding 24 and the winding of relay TR to anode I of tube T, thus forming an anode circuit for the tube. Current is supplied to heat cathode 6 of tube T by connecting one pair I5a and I5b of the four coils of the secondary winding across the cathode of tube T.

With the saturable transformer RT3 arranged and constructed in the manner just described, the inductive coupling of the primary and secondary windings is varied in accordance with the supply of current to saturation winding 24. Normally, the parts of transformer RT3 are so designed and proportioned that under the most unfavorable ballast conditions, the energy supplied from the transformer secondary to the anode circuit through winding 24 of the transformer and. to the filament of tube T conditions the tube to pass suflicient current to energize relay TR at the desired value. When, however, the ballast resistance increases so that a larger energy level is present in the rails to energize primary winding I3, an increased electromotive force is induced in secondary winding I5 and is applied through winding 24 to the anode circuit of the tube. This increased current flow in winding 24 decreases the permeability of the core to decrease the efiectiveness of the inductive coupling between the transformer primary and secondary windings and as a result the electromotive force induced in winding I5 is reduced. It is readily apparent that by properly designing and proportioning the various elements of transformer RT3, the transformer can be made to supply substantially a constant electromotive force to the anode circuit and to the filament of tube T irrespective of relatively wide ballast resistance variations.

As shown in Fig. 8, compensation for ballast resistance variations may also be effected by employing a three-element electronic device AT which has its grid circuit controlled by energy derived from the track rails and has its anode circuit supplying energy to the track relay TR through the medium of a transformer and a rectifying tube controlled by such transformer. Referring now to Fig. 8, which illustrates for example the track circuit arrangement of Fig. 5 modified in the manner described, the electronic device AT as shown comprises an evacuated container 25 in which are disposed a cathode electrode 26, a control or grid electrode 2'! and a plate or anode electrode 28. A source of unidirectional current is connected across cathode 2G and anode 28 of tube AT in series with primary winding I3 of transformer RTZ, and the fiow of current in this anode circuit is made responsive to traffic conditions in section DE by connecting the secondary winding I5 of receiving transformer RTI across the cathode 26 and grid 2? of the tube. The primary winding of transformer RTI is connected across the rails of section DE, which rails are supplied through the medium of track transformer TT with alternating current, and it follows that the alternating current impressed upon the grid circuit of tube AT when section DE is unoccupied causes such alternating current to be reproduced in kind by the tube and hence causes an alternating current component to be superimposed upon the plate circuit current. The current flow in the anode circuit of tube AT may be additionally controlled by trailic conditions in section D E by connecting the cathode 25 across a portion of winding 13 of transformer RTI, as shown, whereby the cathode is heated to its operating condition in response to trackway energy received from the rails when section D-E is unoccupied. However, although this mode of heating the cathode of tube AT is to be preferred, the cathode may, if desired, be heated continuously by energy supplied from a separate source of energy. The alternating cur-.

rent component of the anode circuit current flowing in the primary winding [3 of transformer RT2, causes electromctive forces to be induced in the secondary windings l8 and ill of such transformer and hence causes energy to be supplied to the cathode of a rectifying tube Tl from secondary winding ii and to the anode circuit of such tube from both, secondary windings iii and ii. As shown, a divided secondary winding i5 is used in conjunction with a full-wave rectifier tube Tl to control relay TR, but if. desired, a single anode or half-wave rectifier tube may be connected in an anode circuit supplied with energy from a secondary winding of the transformer.

With the apparatus of. 8 arranged in the manner described, the parts of such apparatus may be proportioned and designed in such manner that when the energy level present in the rails of section D--E is at its lowest value, efiected under the most unfavorable ballast conditions, the grid circuit of tube AT is so controlled by the energy supplied from transformer RTI that the tube AT is conditioned to operate substantially on the upper knee of its performance curve. Then, as the ballast resistance increases and more energy is supplied from transformer RT t0 the grid circuit of tube AT, a relatively large increase in applied grid voltage results in but little increase in magnitude of anode circuit current. Accordingly, the magnitude of the alternating current component of the anode circuit current of such tube is caused to vary but slightly as the ballast resistance increases, and as a result the magnitude of the electromotive forces induced in the secondary windings of transformer RT? and supplied through tube Tl to relay TR are substantially constant, hence the energization of relay TB, is maintained substantially constant by the apparatus of Fig. 8 irrespective of relatively wide variations. in track ballast resistance.

Another advantage of the apparatus of Fig, 8 is that the use of an amplifying tube AT to control the energization of the track relay enables a relatively small electromotive force supplied to the track rails to be amplified through the medium of the tube to a magnitude sufficient to control the track relay. It can be seen that by interposing a transformer and a rectifier tube between the amplifying tube and the relay, the trackway energy may be applied directly to the grid circuit of the amplifying tube and no biasing grid potential is required since the system is caused to operate in response to an alternating current component superimposed upon a plate circuit current in response to alternating current received from the trackway. It fo1lows,,therefore, that if the elements of tube AT or tube Tl fail or become short circuited, a false clear condition of the apparatus is avoided since under such conditions no alternating current component is present in transformer RT2 so that relay TR is released. It follows, therefore, that the circuit arrangement illustrated in. Fig. 8 inill) corporates the usual circuit safeguards such that a failure of the circuit elements cannot cause a false clear condition of the track relay.

Although I have herein shown and described only a few forms of railway track circuit apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. A railway track circuit comprising the combination with a stretch of railway track having means for supplying trackway energy to the track rails of said stretch, of an electronic device having two electrodes one of which-must be energized in order to condition such device to pass current between its electrodes, means for impressing an electromotive force across said two electrodes, means controlled by energy derived from said track rails for energizing said one electrode, and a control device controlled by the current flow between said two electrodes as created by said electromotive force.

2. A railway track circuit comprising the combination with a stretch of railway track having means for supplying trackway energy to the track rails of said stretch, of a thermionic tube having two electrodes one of which must be heated to render the tube conducting, means for heating said one electrode of said tube in response to energy derived from said track rails, a relay, and a circuit for said relay including a source of electromotive force connected across said two electrodes of said tube.

3. A railway track circuit comprising in combination with a section of railway track having means for supplying trackway energy to the rails of said section, an electronic device having two electrodes one of which must be heated to render the device conducting, means for heating said one electrode with energy derived from the rails of said section, means for impressing an electromotive force across said two electrodes, and a relay energized by the current flow created across said two electrodes by said elcctromotive force.

4. A railway track circuit comprising in combination with a section of railway track having a source of unidirectional energy connected across the track rails at one end of the section, an electronic device having two electrodes one of which must be heated to render the device conducting, means for connecting said one electrode across the track rails at the other end of said section, a relay, and a circuit for said relay including a source of current connected across said two electrodes of said device.

5. -A railway track circuit comprising in combination with a section of railway track having means for supplying trackway energy to the rails of said. section, an electronic device having two electrodes one of which must be heated to render the device conducting, means for heating said one electrode with energy derived from the rails of said section, means for impressing across said two electrodes an electromotive force also derived from the rails of said section, and a relay energized by the current flow created across said two electrodes by said electromotive force.

6. A railway track circuit comprising, in combination, a section of railway track having means for supplying alternating trackway; energy to the rails of the section, an electronic tube having two electrodes one of which must be heated to render the tube conducting, means for coupling said one electrode with said rails to receive heating energy from the rails of said section, a relay, and a circuit for said relay including a source of current connected across said two electrodes of said tube.

'7. A railway track circuit comprising in combination with a section of railway track having means for supplying alternating trackway energy to the rails of the section, an electronic tube having two electrodes one of which must be heated to render the tube conducting, means for coupling said one electrode with said rails to receive heating energy from the rails of said section, a relay, and means including the winding of said relay for impressing across said two electrodes an electromotive force derived from said rails.

8. A railway track circuit comprising in combination with a section of railway track having means for supplying trackway energy to the rails of said section, a half-wave rectifier tube having two electrodes one of which must be energized to render such tube conducting during the interval that the other electrode is positive with respect to said one electrode, means for supplying heating energy derived from the rail of said section to said one electrode, a relay and a source of current, and circuit means for connecting the winding of said relay across said two electrodes in series with said source with the source poled in such manner as to at times render said other electrode positive with respect to said one electrode.

9. In combination, a section of railway track having means for supplying to the track rails alternating trackway current, a full-wave rectifier tube having three electrodes one of which must be heated in order to render said tube effective'to pass current between said one electrode and such other of the remaining electrodes as is positive with respect to said one electrode, means for sup-plying heating energy derived from the track rails of said section to said one electrode, means for impressing an alternating electromotive force derived from the track rails across said one electrode and each of the remaining two electrodes in such manner as to cause said two electrodes alternately to become positive with respect to said one electrode, and a relay interposed in circuit with said last-mentioned means and energized by the full-wave rectified current flowing in such circuit.

10. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube effective to pass current of a predetermined value between said two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means for supplyingtosaidone electrode heating energy derived from the track rails, a relay, means including the winding of said relay for applying an electromotive force of said given magnitude across said two tube electrodes, and means responsive to the energy level present in said rails for limiting the magnitude of the electromotive force applied across said two electrodes whereby to maintain said relay energized at a substantially constant energy level irrespective of relatively wide variations of resistance of the track ballast.

11. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube effective to pass current of a predetermined value between said two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means for supplying to said one electrode heating energy derived from the track rails, a relay, a magnetizable core provided with a coil, means including said coil and the .winding of said relay for applying an electromotive force of said given magnitude across said two tube electrodes, and means responsive to the flux condition established in said core in response to the energization of said coil for limiting the magnitude of energy available to energize said relay whereby to maintain a substantially constant energy level in said relay irrespective of relatively wide variations in track ballast resistance.

12. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube effective to pass current between its two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means for heating said one electrode of said tube in response to energy derived from the track rails, a relay, means including the winding of said relay for applying across said two tube electrodes an electromotive force of said given magnitude, a coil interposed in circuit with said relay winding, and a variable inductance connected across said track rails in shunt to said relay and controlled in response to the energization of said coil to render portions of the trackway energy present in the track rails ineffective to influence the heating of said one tube electrode.

13. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube effective to pass current of a predetermined Value between its two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means including the primary winding of a transformer connected across the track rails at the other end of said section for heating said one electrode of said tube, an impedance connected across the track rails in shunt with said transformer primary winding, a relay, means including the winding of said relay for impressing across said two tube electrodes an electromotive force of said given magnitude, and means responsive to the energization of said relay for varying the magnitude of energy shunted by said impedance away from said transformer primary winding, said impedance being controlled in such manner that under low resistance ballast conditions relatively little energy is shunted away from said transformer primary winding but as the ballast resistance increases more energy is shunted whereby the energy level created in the track relay is maintained substantially constant irrespective of relatively wide variations in track ballast resistance.

14. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube efiective to pass current between its two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means including the primary winding of a transformer connected across the track rails at the other end of said section for heating said one electrode of said tube, a saturable reactor having a main winding and a control winding both mounted on a magnetizable core, means for connecting the main winding of said reactor across the track rails at said other end of the section in shunt to said transformer primary winding, a relay, and means including the winding of said relay and the control winding of said reactor for impressing across said two tube electrodes an electromotive force of said given magnitude, the parts of said reactor being so proportioned that when the track ballast resistance is high the flux created in said core due to the current in said control winding substantially saturates such core.

15. In combination, a section of railway track, a source of alternating current connected across the track rails at one end of said section, a relay receiving energy from the track rails at the other end of said section, an inductance connected in shunt to said relay, and means responsive to the current energizing said relay for varying the impedance of said inductance inversely with respect to track ballast resistance variations.

16. In combination, a section of railway track having a source of alternating current connected across the track rails at one end of the section,

a relay, a reactor having a magnetizable core upon which are mounted a control winding and a main winding, means including the control winding of said reactor for coupling said relay with the rails of said section, and means for connecting the main winding of said reactor with the track rails in shunt to said relay, the parts of said reactor being so proportioned that the magnetic flux created in the core due to current in said control winding varies the impedance of said main winding inversely as the track ballast resistance varies.

17. In combination, a section of railway track having a source of alternating current connected across the track rails at one end of the section, a transformer having a magnetizable core carrying a primary winding and a secondary winding and a control winding, said primary winding being connected across the track rails at the other end of said section, a thermionic tube having two electrodes one of which must be heated to render the tube effective to pass current between said two electrodes in response to an electromotive force of a given magnitude applied across said two electrodes, means for connecting said one electrode of said tube with a portion of the secondary winding of said transformer, a relay, and

when the ballast resistance in said section is low the inductive coupling of said transformer primary and secondary windings is controlled by the flux created, by current in sai control Wind'- ing in such manner that an electromotive force of said. given magnitude is applied across said two tube electrodes.

18. In combination, a section of railway track having a source of alternating current connected with the rails at one end of the section, a transformer having a magnetizable core carrying a primary winding and a secondary winding and a control winding, said primary winding of the transformer being connected with the track rails at the other end of said section, a relay, and circuit means including the control winding of said transformer for connecting the winding of said relay across the secondary winding of said transformer, the parts of said transformer being so proportioned that the inductive coupling of the transformer primary and secondary windings is controlled: by the flux created in said control winding due to current in said control winding to vary inversely as the ballast resistance in said section varies.

19. In combination, a section of railway track having a source of alternating current connected with the track rails, a three-element electronic device having a cathode and a grid and an anode electrode, means for connecting the grid and cathode electrodes of said electronic device with the track rails, a source of unidirectional current, a transformer, means including a primary winding of said transformer for connecting said source across the anode and cathode electrodes of said electronic device, a rectifying device, and a relay connected through saidv rectifying device to the secondary winding of said transformer, the connection of the grid and cathode electrodes of said electronic device with the track rails being so proportioned that when the ballast resistance in said section is low the electronic device is caused to operate substantially at the point of maximum amplification.

20. In combination, a section of railway track having a source of energy connected with the track rails, a three-element electronic device having a cathode and a grid and an anode electrode, means for heating the cathode electrode of said tube with energy derived from said track rails, a source of alternating current connected across the cathode and grid electrodes of said tube, a plate circuit for said tube including a source of unidirectional current impressed across the oathode and anode electrodes of said tube, a relay, and means for energizing said relay in response to the alternating current component superimposed upon the plate circuit current when and only when said tube cathode is heated by energy derived from the track rails.

BERNARD E. OHAGAN. 

